Hormone replacement therapy and breast cancer incidence in Korean women

Objectives: After the 2002 Women's Health Initiative (WHI) study, the global use of menopausal hormone therapy (MHT) declined, and despite subsequent studies indicating a low risk of breast cancer, concerns about MHT usage persist. We examined the relationship between changes in MHT use and changes in the incidence of breast cancer from 2002 to 2020 in South Korea. Study design: This study used tumor registry information from 2002 to 2020 from the Korean Statistical Information Service and analyzed the incidence rate of invasive breast cancer in women, who were divided into two age groups: <50 and >50 years. The numbers of MHT prescriptions in Korea between 2002 and 2020 was determined from pharmacy data. Results: The incidence of breast cancer per 100,000 women in South Korea increased from 34.3 in 2002 to 96.4 in 2020. Breast cancer incidence rates increased annually in both groups of women (those aged under and over 50 years), with no significant difference between the two (p = 0.614). Prescriptions for estrogen therapy (ET) in 2020 were 52.7 % lower than those in 2002. Prescriptions for estrogen -progesterone therapy (EPT) decreased by 27.9 % over the same period. Conversely, tibolone prescriptions, which had initially decreased by 25.4 % in 2004, subsequently showed a steady increase and were 93.6 % higher in 2020 than in 2002. Conclusion: The incidence of breast cancer increased annually in Korean women of all ages; however, the use of ET and EPT for MHT has declined since 2002, particularly the use of EPT after 2010. MHT, especially EPT, did not significantly increase the incidence of breast cancer in Korean women.